(a) Field of the Invention
This invention relates to a solid electrolyte and, more particularly, to a glass-polymer composite electrolyte which has a relatively high mechanical flexibility, ion conductivity and stability for lithium batteries.
(b) Description of the Related Art
Lithium is the lightest metal and has a high electronegativity. Therefore, lithium can be used to produce a cell having a large current capacity per unit of mass and high voltage. However, a lithium battery has a stability problem because of reactivity between the lithium metal and a liquid electrolyte. To overcome this problem, a lithium ion battery using a material allowing intercalation and deintercalation of lithium ions for an anode has been developed. And a lithium polymer battery, which uses a solid polymer electrolyte instead of the liquid electrolyte, has been developed. But the solid polymer electrolyte, such as poly(ethylene oxide) and poly(propylene oxide), have a relatively low ion conductivity. The solid electrolyte is easily crystallized at 70.about.80.degree. C., its ion conductivity decreases steeply.
A glass electrolyte is one of solid electrolytes for the lithium battery. It is difficult to handle because of its glass phase. It is liable to crack in charging/discharging. It can be applied to only a non-rechargeable lithium battery and not be applied to a rechargeable lithium battery.
In recent years, to overcome these problems of the polymer electrolyte and the glass electrolyte, a glass-polymer composite electrolyte consisting of B.sub.2 S.sub.3 --Li.sub.2 S--Lil and poly(ethylene oxide)--LiN(CF.sub.3 SO.sub.2).sub.2 has been proposed (Jaephil Cho and Meilin Liu, Georgia Institute of Technology, Electrochimica Acta, Vol. 42, No.10, pp 1481-1488, 1997). But the glass-polymer composite electrolyte has a drawback in that the glass electrolyte and polymer electrolyte react each other. Furthermore, H.sub.2 O molecules in the polymer electrolyte react with the glass electrolyte. A method of preparing B.sub.2 S.sub.3 is very complex. Pure B.sub.2 S.sub.3 is difficult to prepare. B.sub.2 S.sub.3 has a very low stability under oxygen gas atmosphere.